Drag and drop on container page.

STUD-1309
dnd container page styling
Switch the container page to use the new view
Restore the ability to drag at any level inside a vertical and clean up templates.
Update unit test based on changes in master.
fix for Studio 404 and 500 page layouts
STUD-864
Only show drag handles in draft mode
Bok choy acceptance test for drag and drop.
Allow for no runtime_type in the context.
Fix Jasmine tests

Also, rewrite them to be easier to comprehend, and to not use magic constants (or to use fewer, at least).
Clean up coverage and code quality issues
Test cleanup.
Address Christina's review comments
Merge pull request #3229 from edx/christina/container-dnd

Drag and drop on container page
Merge pull request #3577 from edx/frances/fix/404-and-500-page-layout

Fix for Studio 404 and 500 page layouts
STUD-864
Tolerance expressed in percentage now computes correctly. [BLD-522]
Modified and extended tests on percentage expressed tolerance.
Addressed comments.
All tests pass now.